Medical editor

Multiple myeloma

Multiple myeloma is the malignant growth of plasma cells. Plasma cells are B lymphocytes specialized for production of immunoglobulines. It is assumed that the malignant transformation occurs in a cell that has been through maturation in germinal centers of the spleen or a lymph node.

A characteristic of multiple myeloma is the increase of monoclonal plasma cells in the bone marrow, which produce monoclonal gammaglobulin (paraprotein), or sometimes only light or heavy monoclonal chains.

Plasma cells produce immunoglobulins, each clone their own immunoglobulin. A plasma cell clone which grows uncontrollably can produce large amounts of immunoglobulin. This can be diagnosed using electrophoresis of serum or urine, where the monoclonal component (M-component) can be seen as a peak. The M-component is a relative and indirect indicator of the activity/size of the clone and is important for the diagnosis and evaluation of treatment response.

When myeloma cells proliferate in the bone marrow, they may suppress the production of normal blood cells and lead to low hemoglobin (anemia), reduced immune defense (enhanced susceptibility to infections), or low number of thrombocytes (increased risk of bleeding). They may also affect the balance between bone breakdown and bone build-up and give rise to areas of low bone density (osteolytic lesions) which may lead to fractures. The immunoglobulin produced by the myeloma cells can have various properties. Some of these proteins can give rise to deposits in tissues and lead to organ damage, for instance, influence the renal function.

The disease is progressive and is sometimes diagnosed before symptoms develop. Curative treatment for myeloma is rarely possible, but for the last 10-15 years, several new drugs have been developed, which have currently nearly doubled the survival rate.

Cytokine production in the disease process mutually influences the various bone marrow cells: between malignant plasma cells, stroma cells, osteoblasts, and osteoclasts. This causes expansion of the malignant clone, osteolysis of cortical bone, possibly with subsequent pathological fractures that may cause significant pain.

Simultaneously, the production of normal hematopoetic tissue is suppressed which eventually leads to bone marrow failure with pancytopenia.

Incidence

Myeloma is more common in men than women and represents 1.8% of all new cancer cases in the United States. Approximately 0.8% of men and women will be diagnosed with myeloma at some point during their lifetime. Myeloma is most frequently diagnosed among people aged 65-74. In 2017, it is estimated to be 30,280 new cases of myeloma in the United States (1).